Which of the following contributed most to increased settlement of the great plains? a. the discovery of precious metals b. a series of federal land grants c. the availability of buffalo d. a decrease in agricultural production

Answer is: b.a series of federal land grants.
Congress passed a law allowing people to claim public land and convert it to private property through homesteading.
The Great Plains is the broad expanse of flat land that lies west of the Mississippi River tallgrass prairie states and east of the Rocky Mountains in the United States and Canada. 

The american civil war